Microwave antenna feed



Feb. 18, 1958 R. F. OHLEMACHER 2,824,305

MICROWAVE ANTENNA FEED Filed Sept. 50, 1954 Has. 6' Z F1624.

m [hiii 27 INVENTOR RIOHARD E OHLEMACHER G ma United States atent O MICROWAVE ANTENNA FEED Application September 30, 1954, Serial No. 459,564

Claims. (Cl. 343-776) The present invention relates generally to directive antennas; more particularly it relates to an improved feed for microwave directive antenna systems of the type employing parabolic reflectors.

It is a well known microwave radio technique to employ a parabolic reflector for obtaining a sharply directive beam of electromagnetic energy. It is also common practice to utilize a waveguide for conducting microwave energy to the reflector. Since the energy feeding waveguide is ordinarily projected through the reflector axially thereof and from its convex side, some means must be employed to direct the energy from the open end of the waveguide to the reflector for projection thereby as a beam. This directing means usually takes the form of a feed constituted by a head receiving the outer end of the waveguide and having means for reversing the direction of the waves transmitted by the waveguide, whereby they will be projected to the parabolic reflector. One of the problems encountered with the above-described feed structure has been that the feed itself, by reason of its location in the beam projected by the reflector, produces a shadow which results in distortion of the directive pattern of said beam, with resultant production of undesirable side lobes.

One of the principal objects of the present invention, therefore, is to provide a feed for microwave directive antenna systems which will correct the undesirable conditions above described.

A more specific object of the invention resides in the provision of a microwave antenna feed which will emit a portion of the energy received from the waveguide in a forward direction for filling out the pattern and thus eliminating side lobes and other shadow effects.

A further object of the invention is to provide a feed for microwave antenna systems which is simple in construction and which may be applied to said systems without modification thereof.

And another object is to provide a feed having means for effectively isolating the energy emitting apertures from the wall of the waveguide, for assuring a proper impedance match between said waveguide and the feed.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

Fig. 1 is a perspective view of the improved feed for microwave antenna systems as it would appear installed on a section of waveguide;

Fig. 2 is an enlarged longitudinal sectional view;

Fig. 3 is a sectional view on the line 33 of Fig.2;

Fig. 4 is a front elevation of the improved feed; and

Fig. 5 is an elevation, partially diagrammatic, showing the improved feed as a part of a radar system.

Referring now to the drawings in more detail, a section of waveguide of conventional rectangular cross-section is shown at 10. The waveguide section 10 is conventionally mounted in a parabolic reflector A (Fig. 5) with 2,824,305 Patented Feb. 18, 1958 its outer end disposed along the axis of the reflector and at the focal point thereof.

The improved feed constituting the subject matter of the present invention includes a body 12 which is of generally cube shape and is provided with front and rear faces 12a and 12b, respectively.

As best seen in Fig. 2, the body 12 is formed with a central opening 14 which is enlarged to define a recess 15 which terminates in a shoulder 16. The recess 15 receives the outer end portion of the waveguide section 10, the shoulder 16 providing a stop for said section. As will be seen in Fig. 2, the recess is relatively shallow but of such depth that the inner surfaces of the waveguide section 10 will lie in the same planes with the mating surfaces of the central opening 14, so as to provide a smooth, uninterrupted passage for waves traveling through said waveguide into said body 12.

. The central opening 14 diverges near the front face 12:: of the body 12 to define a pair of branches 18 and 19 which are each of the same width but one-half the height of said central opening 14. That is, as will be clearly seen in Fig. 2, the opening 14 is divided and the branches 18 and 19 are directed through substantially and terminate in straight sections 20 and 21 open at their corresponding free ends to define emitter openings 22 and 23 at the rear face 12b. The sections 20 and 21 lie in planes parallel to the plane containing the waveguide section.

Formed in the body 12 between the straight sections 20 and 21 and the central opening 14 are slots which define chokes 24 and 25, the purpose for which will be explained in more detail hereinafter.

At 26 and 27 are shown rectangular slots which communicatc between the front face 12a and the branches 18 and 19 respectively. In operation, electromagnetic energy is caused to travel along the waveguide section 10 by a transmitter B (Fig. 5). Said energy will pass from the waveguide into the central opening 14 and will be divided therein and caused to pass about the branches and be projected from the emitter openings 22 and 23 to illu minate the reflector C (Fig. 5). The reflector C will, in a conventional manner, project the energy forwardly in a predetermined pattern. A portion of the energy entering the body 12 of the feed will be emitted through the slots 26 and 27 and thus projected directly forwardly. This energy will cooperate with that reflected by the reflector, with the result that the shadow which would ordinarily be present because of the existence of the feed in the reflected beam, will be eliminated. The slots 26 and 27 are of such size that the power emitted by them will have an amplitude and phase approximately the same as that masked by the feed itself.

The chokes 24 and 25 effectively isolate the waveguide section 10 from the straight sections 20 and 21 and the openings 22 and 23, with the result that impedance mismatch will be eliminated.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A feed for microwave directive antenna systems, including a body for installation on a waveguide and having front and rear faces, said body having a central opening in its rear face receiving an end of said waveguide, said opening extending forwardly from the rear face and having diverging rearwardly directed branches terminating in emitter openings, slots in the body between the emitter openings and the central opening for defining chokes, and a slot communicating between the front face of the body and each of the branches.

2. In combination with a microwave directive antenna system having a reflector, a waveguide mounted in the reflector, and a source of electromagnetic energy, a feed including a body mounted on the free end of the waveguide, said body having front and rear faces and acentral opening extending forwardly from the rear face and, diverging to provide rearwardly directed branches terminating in emitter openings, a slot communicating between the front face of the body and each of'said branches, said emitter openings directing electromagnetic energy from the source toward the reflector for reflection thereby in a beam pattern surrounding the body, whereby said body will mask a portion of said beam to define a shadow in the pattern, said slots emitting energy forwardly for filling said shadow to complete said pattern, and slots in the rear face of the body and extending inwardly of said body parallel to the central opening to define chokes.

3. The combination recited in claim 2, including slots in the body between the emitter openings and the central opening and extending inwardly from the rear face and parallel to the central opening to define chokes.

4. The combination recited in claim 3, including a recess receiving a portion of said waveguide, and a shoul' der providing a stop for said waveguide.

5. A feed for microwave directive antenna systems ineluding a body for installation on a waveguide, said body being of rectangular shape and including front and rear faces and a central opening for receiving the waveguide, said central opening extending forwardly from the rear face and having branches each diverging and extending through a semi-circular are and terminating in a straight section communicating with the rear face at an emitter opening, a slot in the body between each of the straight sections and the central opening and communicating with the rear face and defining a choke, and a slot communicating between each of the branches and the front face of the body, said emitter openings directing portions of energy entering the central opening from the waveguide to a reflector for reflection thereby past the body in a pattern, said body producing a shadow in said pattern, said last-mentioned slots emitting energy forwardly of the body for filling the shadow and completing the pattern.

References Cited in the file of this patent UNITED STATES PATENTS 2,422,184 Cutler June 17, 1947 2,459,768 Cork et al Jan. 18, 1949 2,556,087 Iams June 5, 1951 

